Conventionally, a valuable sheet article such as a paper sheet or a photograph is usually covered with a protective film for protection because such an article is readily suffered from damage. Typically, a laminator is used for laminating a sheet article between two pieces of plastic films.
FIG. 1A and FIG. 1B are schematic cross-sectional views of a conventional laminator. Hereinafter, operations of the conventional laminator will be illustrated in more details with reference to FIG. 1A and FIG. 1B. The laminator 1 principally comprises an entrance channel 10, a first heating roller 11, a second heating roller 12, a heating unit 13 and an exit channel 14. After the laminator 1 is powered on, the heat offered by the heating unit 13 is transferred to the first heating roller 11 and the second heating roller 12 in order to perform a preheating operation. In the preheating stage, the first heating roller 11 is rotated in a second direction R2 and the second heating roller 12 is rotated in a first direction R1, wherein the first direction R1 is opposed to the second direction R2. Upon rotation of the first heating roller 11 and the second heating roller 12, the heat offered by the heating unit 13 may be more uniformly transferred to the first heating roller 11 and the second heating roller 12. After the preheating operation is completed, a laminated object 15 of a sheet article 15C intervening between a first plastic film 15A and a second plastic film 15B is fed into the laminator 1 through the entrance channel 10. Next, the laminated object 15 is transported by the first heating roller 11 and the second heating roller 12 while both sides of the laminated object 15 are heated and pressed by the first heating roller 11 and the second heating roller 12. During the laminated object 15 is heated and pressed by the first heating roller 11 and the second heating roller 12, the first plastic film 15A and the second plastic film 15B are thermally softened and thus the sheet article 15C is laminated between the first plastic film 15A and the second plastic film 15B. After the laminated object 15 is ejected from the exit channel 14, the laminating operation is completed.
The laminator 1, however, still has some drawbacks. For example, if the laminated object 15 of the sheet article 15C intervening between the first plastic film 15A and the second plastic film 15B is fed into the laminator 1 in the preheating stage, the laminated object 15 will be transported by the first heating roller 11 and the second heating roller 12 because the first heating roller 11 is rotated in the second direction R2 and the second heating roller 12 is rotated in the first direction R1. Since the temperature of the heating roller 11 or 12 is not enough to perform the heating and pressing operation, the first plastic film 15A and the second plastic film 15B transported across the heating rollers 11 and 12 are not sufficiently softened. Under this circumstance, the sheet article 15C fails to be successfully laminated between the first plastic film 15A and the second plastic film 15B or some hazy bubbles are readily formed in the resulting structure to blur the sheet article 15C.
For enhancing the performance of the laminator, there is a need of providing a proper protecting mechanism to prevent from feeding the laminated object into the laminator before the heating rollers reach the working temperature required for performing the heating and pressing operation.